This invention relates generally to flow meters used in the downhole environment. Specifically, this invention relates to downhole flow meters that operate by measuring the pressure drop across a variable orifice valve.
Downhole flow metering is an essential component of reservoir monitoring. As the industry has moved toward permanent monitoring and control in real time, flow rate, pressure, temperature, resistivity, and watercut, among others, have become important components for assessing well performance.
To measure flow rates, a variety of sensors either on a standalone basis or in combination have been deployed. These include spinner tools, venturis, gradiomanometers, electromagnetic, acoustic, tracer detectors and gamma-ray sensors. However, these tools are expensive. Permanent downhole deployment of these sensors, especially when individual zone flow rates in multi-zone wells are desired, would require a large monetary investment.
Flow rate measurements may be used for a variety of purposes. The primary use is to help in quantifying produced fluids. In wellbores having multiple completions with feedback control, it may be desirable to set flow rates or pressure for the various zones so as to optimize the productivity. It is then necessary to measure the flow or pressure rate in each zone, compare them to a set point, and adjust the aperture openings in the valves of each zone completion in order to maintain flow rate or pressure as close to the desired value as possible.
This invention comprises the use of a variable orifice valve as a flow controller and flow meter. Pressure measurements are taken upstream and downstream of the variable orifice valve (across the valve) by way of a differential pressure measurement mechanism. The differential pressure measurement mechanism may comprise two separate absolute pressure measurement devices or a single differential pressure measurement device. Flow rate through the valve is determined from the pressure drop across the valve. In wellbores having multiple zones, a variable orifice valve together with a differential pressure measurement mechanism may be deployed for each zone. The flow rate through each of the zones, in the completion tubing, and at the surface can then be monitored and controlled.